#!/usr/bin/env python3

# Contest Management System - http://cms-dev.github.io/
# Copyright © 2012-2017 Luca Wehrstedt <luca.wehrstedt@gmail.com>
# Copyright © 2013 Stefano Maggiolo <s.maggiolo@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import os
import sys
import time
from datetime import datetime

import babel.dates


__all__ = [
    "make_datetime", "make_timestamp",
    "get_timezone", "get_system_timezone",

    "utc", "local_tz",
    ]


def make_datetime(timestamp=None):
    """Return the datetime object associated with the given timestamp.

    timestamp (int|float|None): a POSIX timestamp, or None to use now.

    return (datetime): the datetime representing the UTC time of the
        given timestamp.

    """
    if timestamp is None:
        return datetime.utcnow()
    else:
        return datetime.utcfromtimestamp(timestamp)


EPOCH = datetime(1970, 1, 1)


def make_timestamp(_datetime=None):
    """Return the timestamp associated with the given datetime object.

    _datetime (datetime|None): a datetime object, or None to use now.

    return (float): the POSIX timestamp corresponding to the given
        datetime ("read" in UTC).

    """
    if _datetime is None:
        return time.time()
    else:
        return (_datetime - EPOCH).total_seconds()


utc = babel.dates.UTC
local_tz = babel.dates.LOCALTZ


def get_timezone(user, contest):
    """Return the timezone for the given user and contest

    user (User): the user owning the timezone.
    contest (Contest): the contest in which the user is competing.

    return (tzinfo): the timezone information for the user.

    """
    if user.timezone is not None:
        try:
            return babel.dates.get_timezone(user.timezone)
        except LookupError:
            pass
    if contest.timezone is not None:
        try:
            return babel.dates.get_timezone(contest.timezone)
        except LookupError:
            pass
    return local_tz


def get_system_timezone():
    """Return the name of the system timezone.

    return (unicode): the "best" description of the timezone of the
        local system clock that we were able to find, in a format like
        "Europe/Rome", "CET", etc.

    """
    if hasattr(local_tz, 'zone'):
        return local_tz.zone
    return local_tz.tzname(make_datetime())